In vitro antiandrogenic effects of the herbicide linuron and its metabolites

Although the herbicide linuron is banned for use in the EU due to its reproductive and developmental toxicity, it can still be found in randomly sampled foods grown in and outside the EU. It is not clear if metabolites of linuron can contribute to the endocrine disrupting effects following exposure to the parent compound. To address this gap, we analysed linuron and the metabolites 1-(3,4-dichlorophenyl) urea (DCU), 3,4-dichloroaniline (DCA) and 1-(3,4-dichlorophenyl)-3-methoxyurea (DCXU) for androgen receptor (AR) activities and effects on steroidogenesis. Generally, linuron and the metabolites showed qualitatively similar antiandrogenic profiles, but potencies varied. All compounds were AR antagonists, with linuron showing highest potency (IC50 of 2.8 μM). The overall picture of effects on steroidogenesis showed that linuron and metabolites increased the levels of estrogens and corticosteroids, whereas the synthesis of androgens was inhibited. The metabolite DCU was by far the most potent inhibitor of testosterone synthesis (IC50 of 6.7 μM compared to IC50 of 51.1 μM for linuron). We suggest that it is likely that the metabolites contribute to the antiandrogenic effects of linuron in vivo, especially by inhibiting testosterone synthesis.

Nanostructured graphitic carbon nitride (g-C3N4)-CTAB modified electrode for the highly sensitive detection of amino-triazole and linuron herbicides

In agro-areas, linuron (LNR) and amino-triazole (ATZ) are the widely used herbicides to protect crops, but their widespread use pollutes the environment, especially when these are mixed with water or soil. In efforts to address these environmental issues and to detect trace quantities of the herbicides, a graphitic carbon nitride (g-C₃N₄) with cetyltrimethylammonium bromide (CTAB) modified carbon paste electrode (g-C₃N₄-CTAB/CPE) was developed and used for the detection of LNR and ATZ. Materials were characterized by XRD, TEM and AFM techniques. The effect of pH on electro-oxidation (under optimized conditions) showed the maximum peak current at pH of 4.2 for AMT and pH 6.0 for LNR. The electro-kinetic and thermodynamic parameters of LNR and ATZ were determined. Additional experiments were performed for the trace level detection of ATZ and LNR using the square wave voltammetric technique. Concentrations were varied linearly in the range of 3.0 × 10^-7 M to 4.5 × 10^-5 M for ATZ with a detection limit of 6.41 × 10^-8 M, and 1.2 × 10^-7 M to 3.0 × 10^-4 M for LNR with a detection limit of 2.47 × 10^-8 M. The developed novel sensor was effective for trace level detection of LNR and ATZ in water and soil samples.

Analysis of herbicide and its applications through a sensitive electrochemical technique based on MWCNTs/ZnO/CPE fabricated sensor

The electrochemical performance of linuron (LNR) was studied by fabricating the carbon paste electrode (CPE) using multiwalled carbon nanotubes (MWCNTs) along with zinc oxide (ZnO) nanoparticles (MWCNTs/ZnO/CPE). The influence of electro-kinetic specifications involving steady heterogeneous rate, pH, sweep rate, temperature effect, transfer coefficient, accumulation time, activation energy, as well as the total number of protons and electrons participating in electro-oxidation of LNR has been established using voltammetric techniques like cyclic voltammetry (CV) and square wave voltammetry (SWV). These techniques were applied to investigate LNR in real samples such as soil including water samples. Over the 0.02 μM-0.34 μM ranges, a linear relationship was confirmed along with the limit of detection and quantification (LOD and LOQ) of the LNR. The synthesized ZnO nanoparticles were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) analysis. The MWCNTs/ZnO/CPE sensor was considered sensitive for LNR detection because the sensor exhibited enhanced catalytic qualities with peak current in the involvement of 0.2 M phosphate buffer solution (PBS) of pH 6.0, attributed to the ultimate sensing performance of the sensor.

Conformational analysis and concentration detection of linuron: Spectroscopic NMR and SERS study

Linuron is a commonly used organic herbicide which is used in plant growth control. Due to its potential health concerns, the characterization and monitoring of linuron have been a subject of several studies. In this work, we employed nuclear magnetic resonance (NMR) and Raman spectroscopic techniques supported with the density functional theory (DFT) to investigate the conformational behavior and electronic aspects of linuron. The selective nuclear Overhauser effect (SelNOE) spectra confirmed that linuron exists predominantly in the anti configuration and is facilitated with a weak intramolecular hydrogen bonding between the acidic amide proton and oxygen of methoxy moiety. Quantum chemical results showed that the corresponding syn form of the molecule is 8.5 kcal/mol less stable. Further, the surface enhanced Raman scattering (SERS) technique using gold nanoparticles (AuNPs) was implemented as a potential spectroscopic protocol for the concentration monitoring of trace linuron. The Raman responses of four vibrational modes, namely CC stretching, CN stretching, N-H rocking and ring deformation, were successfully enhanced with an excellent linear concentration-intensity dependency. The aromatic CC stretching vibration at 1595 cm^-1 in the Raman spectra has demonstrated the highest enhancement factor (6.5 × 10⁴) and the lowest limit of detection (10^-7 M). The interaction of linuron with the gold nanocluster was simulated by establishing a simple DFT model which predicted that the most pronounced binding with the gold atom takes place at the benzene ring.

Pesticide-induced multigenerational effects on amphibian reproduction and metabolism

Underlying drivers of species extinctions need to be better understood for effective conservation of biodiversity. Nearly half of all amphibian species are at risk of extinction, and pollution may be a significant threat as seasonal high-level agrochemical use overlaps with critical windows of larval development. The potential of environmental chemicals to reduce the fitness of future generations may have profound ecological and evolutionary implications. This study characterized effects of male developmental exposure to environmentally relevant concentrations of the anti-androgenic pesticide linuron over two generations of offspring in Xenopus tropicalis frogs. The adult male offspring of pesticide-exposed fathers (F1) showed reduced body size, decreased fertility, and signs of endocrine system disruption. Impacts were further propagated to the grand-offspring (F2), providing evidence of transgenerational effects in amphibians. The adult F2 males demonstrated increased weight and fat body palmitoleic-to-palmitic acid ratio, and decreased plasma glucose levels. The study provides important cross-species evidence of paternal epigenetic inheritance and pollutant-induced transgenerational toxicity, supporting a causal and complex role of environmental contamination in the ongoing species extinctions, particularly of amphibians.

Community composition modifies direct and indirect effects of pesticides in freshwater food webs

For environmental risk assessment, the effects of pesticides on aquatic ecosystems are often assessed based on single species tests, disregarding the potential influence of community composition. We, therefore, studied the influence of changing the horizontal (the number of species within trophic levels) and vertical composition (number of trophic levels) on the ecological effects of the herbicide linuron and the insecticide chlorpyrifos, targeting producers and herbivores, respectively. We tested how adding, to a single primary producer, 4 selected competing producer species, 0-1-4 selected herbivore species, and one selected predator species resulting in 1, 2 and 3 trophic levels, changes the effects of the two pesticides. Linuron decreased producer biovolume less (17%) when the 4 producers were added, because insensitive producers compensated for the loss of sensitive producers. However, linuron decreased producer biovolume 42% and 32% more as we increased the number of herbivore species from 0 to 4 and as we increased trophic levels from 1 to 3, respectively. The indirect negative effect of linuron on herbivore biovolume was 11% and 15% lower when more producer and herbivores were added, respectively. Adding a predator increased this indirect negative effect by 22%. Chlorpyrifos decreased herbivore biovolume about 10% less when adding multiple herbivore or producer species. However, adding a predator magnified the direct negative impact on herbivores (13%). Increasing the number of producer, herbivore species and adding trophic levels increased the indirect positive impact on producer biovolume (between 10% and 35%). Our study shows that changing horizontal composition can both increase and decrease the effects of the selected pesticides, while changing vertical composition by adding number of trophic levels always increased these effects. Therefore, single species sensitivity will not always represent a worst case estimate of ecological effects. Protecting the most sensitive species may not ensure protection of ecosystems.

α-lipoic acid protects testis and epididymis against linuron-induced oxidative toxicity in adult rats

Linuron is well known for its antiandrogenic property. However, the effects of linuron on testicular and epididymal pro- and antioxidant status are not well defined. On the other hand, α-lipoic acid is well known as universal antioxidant. Therefore, the purpose of this study was twofold: firstly to investigate whether linuron exposure alters antioxidant status in the testis and epididymis of rats and if so, whether the supplementation of α-lipoic acid mitigates linuron-induced oxidative toxicity in rats. To address this question, α-lipoic acid at a dose of 70 mg/Kg body weight (three times a week) was administered to linuron exposed rats (10 or 50 mg/Kg body weight, every alternate day over a period of 60 days), and the selected reproductive endpoints were analyzed after 60 days. Respective controls were maintained in parallel. Linuron at selected doses reduced testicular daily sperm count, and epididymal sperm count, sperm motility, sperm viability, and number of tail coiled sperm, reduced activity levels of 3β- and 17β-hydroxysteroid dehydrogenases, decreased expression levels of StAR mRNA, inhibition of testosterone levels, and elevated levels of testicular cholesterol in rats over controls. Linuron intoxication deteriorated the structural integrity of testis and epididymis associated with reduced the reproductive performance over controls. Conversely, α-lipoic acid supplementation enhanced sperm quality and improved the testosterone synthesis pathway in linuron exposed rats over its respective control. Administration of α-lipoic acid restored inhibition of testicular and epididymal enzymatic (superoxide dismutase, catalase, glutathione reductase, glutathione peroxidise) and non-enzymatic (glutathione content), increased lipid peroxidation and protein carbonyl content produced by linuron in rats. α-lipoic acid supplementation inhibited the expression levels of testicular caspase-3 mRNA levels and also its activity in linuron treated rats. To summate, α-lipoic acid-induced protection of reproductive health in linuron treated rats could be attributed to its antioxidant, and steroidogenic properties.

Part II: Endocrine-related gene expression assessment on male offspring rat testes

Exposure to endocrine-disrupting compounds (EDCs) during pregnancy and early development can lead to adverse developmental outcomes in offspring. One of the endpoints of concern is feminization. The present study aimed to investigate for any possible correlations with endocrine sensitive parameters in the testes of male rat offspring following dam exposure to three EDCs by assessing the expression of endocrine-related genes. Dienestrol (DIES) [0.37-6.25 μg/kg bw/day], linuron (LIN) [1.5-50 mg/kg bw/day], flutamide (FLU) [3.5-50 mg/kg bw/day] as well as their binary mixtures were administered to sexually mature female rats from gestation day (GD) 6 until postnatal day (PND) 21. Gene expression analysis of Star, Cyp11a1, Cyp17a1, Hsd3b2, Pgr and Insl3 was performed by RT-qPCR. Administration of the anti-androgen FLU alone significantly upregulated Cyp11a1 and Cyp17a1 gene expression while administration of LIN and DIES alone did not alter significantly gene expression. The effects of the binary mixtures on gene expression were not as marked as those seen after single compound administrations. Deregulation of Cyp17a1 in rat pup testis, following administration of FLU alone or in mixtures to dams, was significantly correlated with the observed feminization endpoints in male pups.

Expression of the human gene CYP1A2 enhances tolerance and detoxification of the phenylurea herbicide linuron in Arabidopsis thaliana plants and Escherichia coli

The phenylurea herbicide, linuron (LIN), is used to control various types of weeds. Despite its efficient role in controlling weeds, it presents a persistent problem to the environment. In the current study, phytoremediation properties of transgenic CYP1A2 Arabidopsis thaliana plants to LIN were assessed. CYP1A2 gene was firstly cloned and expressed in bacteria before proceeding to plants. In presence of LIN, The growth of CYP1A2 expressing bacteria was superior compared to control bacteria transformed with the empty bacterial expression vector pET22b(+). No clear morphological changes were detected on CYP1A2 transgenic plants. However, significant resistance to LIN herbicide application either via spraying the foliar parts of the plant or via supplementation of the herbicide in the growth medium was observed for CYP1A2 transformants. Plant growth assays under LIN stress provide strong evidence for the enhanced capacity of transgenic lines to grow and to tolerate high concentrations of LIN compared to control plants. HPLC analyses showed that detoxification of LIN by bacterial extracts and/or transgenic plant leaves is improved as compared to the corresponding controls. Our data indicate that over expression of the human CYP1A2 gene increases the phytoremediation capacity and tolerance of Arabidopsis thaliana plants to the phenylurea herbicide linuron.

Using short-term bioassays to evaluate the endocrine disrupting capacity of the pesticides linuron and fenoxycarb

Several short-term whole-organism bioassays based on transgenic aquatic models are now under validation by the OECD (Organization for Economic Co-operation and Development) to become standardized test guidelines for the evaluation of the endocrine activity of substances. Evaluation of the endocrine disrupting capacity of pesticides will be a domain of applicability of these future reference tests. The herbicide linuron and the insecticide fenoxycarb are two chemicals commonly used in agricultural practices. While numerous studies indicate that linuron is likely to be an endocrine disruptor, there is little information available on the effect of fenoxycarb on vertebrate endocrine systems. Using whole-organism bioassays based on transgenic Xenopus laevis tadpoles and medaka fry we assessed the potential of fenoxycarb and linuron to disrupt thyroid, androgen and estrogen signaling. In addition we used in silico approach to simulate the affinity of these two pesticides to human hormone receptors. Linuron elicited thyroid hormone-like activity in tadpoles at all concentrations tested and, showed an anti-estrogenic activity in medaka at concentrations 2.5mg/L and higher. Our experiments suggest that, in addition to its previously established anti-androgenic action, linuron exhibits thyroid hormone-like responses, as well as acting at the estrogen receptor level to inhibit estrogen signaling. Fenoxycarb on the other hand, did not cause any changes in thyroid, androgen or estrogen signaling at the concentrations tested.

Maternal linuron exposure alters testicular development in male offspring rats at the whole genome level

Linuron is a widely used herbicide; its toxicity on the male reproductive system has been recognized. The current study was designed to explore the molecular mechanism underlying linuron-induced reproductive toxicity. Pregnant rats received daily oral gavage of linuron at the dose of 120mg/kg/d from gestation day (GD)12 to GD17. Tissues from male offspring rats were collected for pathological examination and microarray gene expression profiling. Changes in gene expression were further verified by quantitative real-time RT-PCR. Data showed that linuron-exposed offspring rats had a decreased sperm count (88% of controls) and disrupted acrosome formation. There were evident damages in seminiferous tubules and abnormal morphology in mesenchymal cells in samples from linuron-exposed animals. Microarray analysis indicated that the expressions of testosterone synthesis-associated genes, i.e., Star, P450scc, 3β-Hsd, Abp, Cox7a2, Pcna, p450c17and17β-Hsd were significantly altered by linuron exposure, along with other genes involving in cell proliferation and apoptosis, such as c-myc, S6K, Apaf1, and TSC1. These data indicate that linuron upon entering male offspring body can directly or indirectly interact with the androgen production and function; linuron-induced alteration in genes encoding testosterone synthesis is likely a major factor in linuron-induced male reproductive toxicity.

Study of processes influencing bioavailability of pesticides in wood-soil systems: Effect of different factors

Lignocellulosic wastes and by-products containing lignin are now available in large amounts from forestry and industrial activities, and could be promising organic materials for the biosorption of pesticides by soils in order to reduce point-source pollution. Adding these materials to soil requires understanding the process of pesticide sorption-desorption by wood-soils, as sorption capacity could increase, with changes in pesticide bioavailability and final fate. The objective of this work was to study the effect that pine and oak wood added to soils had on the sorption/desorption of the pesticides linuron, alachlor, and metalaxyl. Experiments were conducted with two sandy loam and sandy clay soils each amended with two wood doses (5% and 50%) after different incubation times (0, 5 and 12 months). A low wood dose (5%) had no significant impact on the sorption (K_f) of alachlor, but K_f increased for linuron (up to 5.4-1.7 times) and metalaxyl (up to 4.4 and 8.6 times) in all wood-soil systems. The results were not significantly different after different incubation times. The desorption results indicated that wood decreases the sorption irreversibility of alachlor, and increases that of linuron and metalaxyl, with a varying effect of the wood-soil incubation time. The addition of a high wood dose to soil (50%) was more significant for increasing the sorption of all the pesticides, and the sorbed amounts remaining after desorption (>49% for linuron, >33% for alachlor and >6% for metalaxyl), although there was no apparent discrimination between the two types of woods. The role of the nature of the organic carbón (K_oc values) for sorption was evidenced for alachlor and metalaxyl, but not for linuron. These outcomes are of interest for extending wood application to soil as a barrier for avoiding environmental risk by point-source pollution due to the use and management of pesticides in farming systems.

Reproductive toxicity of linuron following gestational exposure in rats and underlying mechanisms

Linuron is a widely used herbicide in agriculture; its endocrine disruptive toxicity has recently received public attention. This study was designed to examine the developmental toxicity of linuron on the reproductive system of male offspring following maternal exposure. Mother rats received oral gavages of linuron, once daily, at the dose of 0, 50, 100, 150 or 200mg/kg, from gestational day (GD)13 to GD18; gonadal organs from GD20 fetuses were examined. Data indicated that exposed male offspring had a significantly shortened anogenital distance. Pathological examination further revealed a lack of fusion in the urogenital fold in treated fetuses, the damaged seminiferous tubules, and the injured Leydig cell ultrastructure. Analysis of serum testosterone concentrations at postnatal day (PND)2 showed a significant dose-related reduction (about 33.7-58.75%, r=-0.838, p<0.05) as compared to controls. Immunohistochemical results demonstrated a significantly reduced expression of enzymes pertinent to the testosterone production including P450scc, 3β-HSD, and PCNA in Leydig cells (p<0.05). qPCR studies confirmed decreased levels of mRNAs encoding P450scc, 3β-HSD and PCNA (p<0.05). Taken together, these data suggest that maternal exposure to linuron hampers the male gonadal organ development; this appears to be due to linuron's direct action on the production of testosterone in fetal and postnatal offspring.

Evaluation of 8-hydroxy-2-deoxyguanosine and NFkB activation, oxidative stress response, acetylcholinesterase activity, and histopathological changes in rainbow trout brain exposed to linuron

Linuron is a widely used herbicide to control grasses and annual broad leaf weeds. It is known that linuron has toxic effects on different organisms. However, the toxic effects of linuron on aquatic organisms, especially fish, is completely unknown. Thus, we aimed to investigate changes in 8-hydroxy-2-deoxyguanosine (8-OHdG) and nuclear factor kappa B (NFkB) activity, histopathological changes, antioxidant responses and acetylcholinesterase (AChE) activity in rainbow trout brain after exposure to linuron. Fish were exposed to 30μg/L, 120μg/L and 240μg/L concentrations of linuron for twenty-one days. Brain tissues were taken from fish for 8-OHdG and NFkB activity, histopathological examination and determination of superoxide dismutase (SOD), catalase (CAT) enzyme activity, lipid peroxidation (LPO), and reduced glutathione (GSH) levels. Our data indicated that high linuron concentrations caused a decrease in GSH levels, SOD and CAT activities in brain tissues (p<0.05). LPO levels were significantly increased by 240μg/L linuron. All concentrations caused a significant inhibition in brain AChE enzyme activity (p<0.05). Immunopositivity was detected for 8-OHdG and NFkB, and linuron exposure caused histopathological damage to the brain tissues. The results of this study can provide useful information for understanding of linuron-induced toxicity.

Ionic liquid coated magnetic core/shell Fe3O4@SiO2 nanoparticles for the separation/analysis of linuron in food samples

Three hydrophobic ionic liquids (ILs) including 1-butyl-3-methylimidazole hexafluorophosphate ([BMIM]PF6), 1-hexyl-3-methyl-imidazole hexafluorophosphate ([HMIM]PF6), and 1-octyl-3-methylimidazole hexafluoro-phosphate ([OMIM]PF6) coated Fe3O4@SiO2 nanoparticles with core-shell structure to prepare magnetic solid phase extraction agent (Fe3O4@SiO2@ILs) and establish a new method of magnetic solid phase extraction (MSPE) coupled with UV spectrometry for separation/analysis of linuron. The results showed that linuron was adsorbed rapidly by Fe3O4@SiO2@[OMIM]PF6 and eluanted by ethanol. Under the optimal conditions, preconcentration factor of the proposed method was 10-fold. The linear range, detection limit, correlation coefficient (R) and relative standard deviation (RSD) were found to be 0.04-20.00 μg mL(-1), 5.0 ng mL(-1), 0.9993 and 2.8% (n=3, c=4.00 μg mL(-1)), respectively. The Fe3O4@SiO2 nanoparticles could be used repeatedly for 10 times. This proposed method has been successfully applied to the determination of linuron in food samples.

Various effects of the photosystem II--inhibiting herbicides on 5-n-alkylresorcinol accumulation in rye seedlings

The effect of three PSII-inhibiting herbicides, lenacil, linuron, and pyrazon, on the accumulation of 5-n-alkylresorcinols in rye seedlings (Secale cereale L.) grown under various light and thermal conditions was studied. All used chemicals increased resorcinolic lipid content in both green and etiolated plants grown at 29 °C. At 22 °C pyrazon and lenacil decreased the content of alkylresorcinols in plants kept in the darkness and increased their amount in the light-grown seedlings. In turn, level of resorcinolic lipids was decreased by linuron in both etiolated and green plants. At the lowest tested temperature lenacil enhanced production of alkylresorcinols only in etiolated rye seedlings, whereas the light-independent stimulatory action of pyrazon on alkylresorcinol accumulation in rye grown at 15 °C was observed. Additionally, only the latter did not exert a negative effect on rye seedling growth under any of tested conditions. Compared with respective controls, the herbicides used also markedly modified the qualitative pattern of resorcinolic homologs. Interestingly, the observed changes generally favored the enhanced antifungal activity of these compounds. Our study provides novel information on the influence of PSII inhibitors on alkylresorcinol metabolism in rye seedlings. The unquestionable achievement of this work is the observation that low dose of pyrazon mainly stimulated both growth and alkylresorcinol synthesis in rye seedlings, a non-target plant. Moreover, our experimental work showed unambiguously that the observed pyrazon-driven accumulation and homolog pattern modification of alkylresorcinols dramatically improved the resistance of winter rye to infections caused by Rhizoctonia cerealis.

Voltammetric determination of the herbicide Linuron using a tricresyl phosphate-based carbon paste electrode

This paper summarises the results of voltammetric studies on the herbicide 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (Linuron), using a carbon paste electrode containing tricresyl phosphate (TCP-CPE) as liquid binder. The principal experimental conditions, such as the pH effect, investigated in Britton-Robinson buffer solutions (pH 2.0–7.0), the peak characteristics for the analyte of interest, or instrumental parameters for the differential pulse voltammetric mode were optimized for the method. As found out, the best electroanalytical performance of the TCP-CPE was achieved at pH 2.0, whereby the oxidation peak of Linuron appeared at ca. +1.3 V vs. SCE. The analytical procedure developed offers good linearity in the concentration range of 1.25–44.20 μg mL⁻¹ (1.77 × 10⁻⁴–5.05 × 10⁻⁶ mol L⁻¹), showing—for the first time—the applicability of the TCP-CPE for anodic oxidations in direct voltammetry (without accumulation). The method was then verified by determining Linuron in a spiked river water sample and a commercial formulation and the results obtained agreed well with those obtained by the reference HPLC/UV determination.